This application claims the priority of German application 198 49 914.0, filed in Germany on Oct. 29, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to an internal combustion engine with a separately operable additional valve, in addition to intake and exhaust valves at respective cylinders.
To improve combustion in internal combustion engines and the exhaust emission specification, it is known to recirculate a portion of the exhaust gas.
An internal combustion engine is known from U.S. Pat. No. 5,203,310 that has a separately operable exhaust gas recirculating valve in addition to the intake valves and exhaust valves for the charge changing process, said exhaust gas recirculating valve being located in the cylinder head of the engine. An exhaust gas recirculating line can be controlled by the exhaust gas recirculating valve and runs between an intake port and exhaust port of a cylinder or, alternatively, between the interior of the cylinder and the intake port. The exhaust gas recirculating valve can be opened at the beginning of the intake cycle of the corresponding cylinder. The beginning and duration of the exhaust gas recirculation can be adjusted depending on the desired quantity of exhaust gas to be recirculated and the operating state of the internal combustion engine.
One disadvantage of the internal combustion engine or of the method described consists in the fact that it cannot be used or can be used to only a very limited extent in supercharged engines. In order to achieve exhaust gas recirculation using the method described, the pressure in the intake port must be lower than the exhaust gas pressure in the exhaust port, in other words there must be a negative pressure differential across the internal combustion engine. In supercharged engines, however, especially supercharged diesel engines, except at low partial loads, the boost pressure in the intake port is higher than the exhaust gas pressure in the exhaust port. Exhaust recirculation is not possible.
In addition, an engine with an additional exhaust gas recirculating valve in the cylinder head is known from DE 196 21 530 C1, through which valve the interior of the cylinder can be connected with the exhaust port of the cylinder. In the method described, an exhaust stroke of adjacent expelling cylinders is used in the method described by suitable timing of the exhaust recycling valve. Despite a pressure drop that is positive on average over time between the intake port and the exhaust port, during the exhaust stroke of the adjacent expelling cylinder the pressure in the exhaust line is higher than the boost pressure for a short time, so that exhaust gas flows into the combustion chamber through the open exhaust recirculating valve. The disadvantage of the method is that the recirculated volume of exhaust gas depends on the load and rpm of the engine. The quantity recirculated therefore cannot be adjusted at will at any operating point.
Additional concepts for exhaust gas recirculation in supercharged engines provide for a corresponding throttling of the boost air or the use of ejectors in operating ranges in which the boost pressure is greater than the exhaust gas pressure in order to produce the desired pressure differentials for exhaust gas recirculation. However, these measures are mostly expensive and cumbersome and also cause considerable construction cost and space requirements.
A goal of the invention is to design an internal combustion engine with an additional valve in an economical fashion so that improved exhaust gas emission specifications can be reached, especially in supercharged internal combustion engines.
This goal is achieved according to preferred embodiments of the invention by providing an internal combustion engine comprising a first cylinder, a first intake valve operable to control an intake port of the first cylinder, a first exhaust valve operable o control an exhaust port of the first cylinder, a first additional valve operable to control gas flow from the first cylinder separately from the first intake valve and the first exhaust valve, a second cylinder, a second intake valve operable to control an intake port of the second cylinder, a second exhaust valve operable to control an exhaust port of the second cylinder, a second additional valve operable to control gas flow from the second cylinder separately from the second intake valve and the second exhaust valve, a gas flow line communicating with the first additional valve, and a gas flow control arrangement operable to control gas flow in the gas flow line from the first cylinder to the second cylinder.
The invention takes its departure from the fact that in an engine that can be adjusted especially flexibly, the engine can advantageously be kept close to optimum over a wide operating range, so that the efficiency is increased and the exhaust emission specifications can be improved.
According to the invention, at least a first cylinder is connected by an additional valve through a line directly or indirectly with at least one second cylinder. As a result, gas can be conducted from the first cylinder into the second cylinder and can be varied in terms of composition, pressure, and temperature. Furthermore, over a long time interval, gas can be removed at a high pressure and supplied to one or more cylinders deliberately in a specific cycle, for example in the intake cycle or power stroke. A sufficiently high pressure potential or a corresponding pressure drop can be achieved over the entire operating range, especially in supercharged engines.
Advantageously, exhaust gas can be removed at high pressure for exhaust gas recirculation over a long period of time, with the additional valve opening each time following the end of combustion during the power stroke or the exhaust stroke and closing before the cylinder pressure drops below the pressure on the intake side. The additional valve can thus be opened for almost two power strokes. A sufficiently high exhaust gas pressure, especially for supercharged engines as well, can be achieved over the entire operating range of the engine. The rate of exhaust gas recirculation can be adjusted over the entire characteristic map of the engine.
In the engine according to the invention, the recirculated exhaust gas can also be cooled. A high charge density with a sufficiently large amount of fresh air can be achieved, with fuel consumption being reduced and the exhaust emission specification being improved, especially particle emission.
In order to produce an economical engine overall, the additional valve can be especially favorably used for other functions in addition to exhaust gas recirculation, especially for braking operation of the engine and for producing compressed air. The available parts are used for several functions, saving on parts, construction, and expense.
Additional advantages follow from the description of the drawing below. The drawings show embodiments of the invention. The specification and the claims contain numerous features in combination. The individual skilled in the art will advantageously also consider the features individually and combine them to come up with logical further combinations.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.